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Embracing Energy Efficiency:

Understanding Furnace Choices and Their Impact

As regulations have led to more energy-efficient furnaces, it’s essential to understand their differences and how they impact your energy consumption and overall costs. This article will delve into the various furnace types, their efficiency levels, and how to choose the right one for your home.

Energy Efficiency Ratings and Furnace Types

Furnaces are rated by their annual fuel utilization efficiency (AFUE), which represents the percentage of fuel consumed for heating your home. Modern furnaces have minimum ratings of 78% (for oil) and up to 99% (for gas). The Department of Energy states that heat lost through ducts or pipes can account for as much as 35% of total heating energy. Therefore, choosing a high-efficiency furnace can have a significant impact on reducing energy costs.

Comparing 80% and 95%+ AFUE Furnaces

A standard-efficiency furnace provides 80% AFUE, expelling 20% of the energy produced by natural gas as exhaust. High-efficiency furnaces offer 90% or more AFUE, with many new gas-powered furnaces rated at 95%+ AFUE. The key differences between these two types of furnaces are their combustion methods and associated costs.

An 80% furnace uses open combustion, drawing air from the surrounding area, while a 95% furnace uses sealed combustion, pulling in outdoor air through a dedicated PVC pipe. This difference affects installation costs and safety concerns, depending on your furnace’s location and whether it resides in a vented or unvented environment.

Stages of Heat and Airflow

When evaluating furnace efficiency, it’s crucial to consider the stages of heat and airflow, including single-stage, two-stage, or modulating furnaces, and on/off or variable-speed airflow. Two-stage furnaces with variable airflow can be more energy-efficient than single-stage furnaces, even with a lower AFUE rating.

A fully modulating 97%+ furnace with variable airflow offers the highest energy efficiency, adjusting capacity to match your heating needs at any given time.

Choosing the Right Furnace for Your Home

Here are some general guidelines to help you choose the best furnace for your home:

  1. Replacing an 80% furnace in a vented space: Opt for a new 80% furnace, considering a two-stage unit with variable airflow for increased energy efficiency.
  2. Installing a furnace in an enclosed or encapsulated space: A 95% furnace with a concentric vent is the safer and more efficient choice.
  3. Furnace exhausts into a chimney: A 95% furnace with a new exhaust vent ensures safety and prevents exhaust gases from entering your home. If opting for an 80% model, consider installing a new chimney liner.
  4. Energy efficiency is the top priority: Choose a fully modulating 97%+ furnace with variable airflow.

Keep in mind that upgrading to a more energy-efficient furnace may not always provide a significant return on investment, especially when replacing an 80% furnace in a vented environment. However, any efficiency improvement is a step in the right direction.


Choosing the right furnace for your home depends on factors such as your furnace’s location, energy efficiency goals, and safety concerns. By understanding the differences between various furnace types and efficiency ratings, you can make an informed decision to reduce energy consumption, save money, and create a more comfortable home environment.

Feel free to reach out with any questions or feedback at AskFry@RELYonFRY.com. We’re here to help with all your furnace, air conditioner, plumbing, and backup generator needs for both residential and commercial customers.

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